1/2x-75%=1/4
=>2x-3/4=1/4
=>2x=1/4+3/4
=>2x=1
=>x=1/2
Vậy x=1/2
2,|x-2/3|+0,25=3/4
=>|x-2/3|+1/4=3/4
=>|x-2/3|=3/4-1/4
=>|x-2/3|=1/2
=>x-2/3=1/2 hoặc x-2/3=-1/2
=>x=1/2+2/3 hoặc x=-1/2+2/3
=>x=7/6 hoặc x=1/6
3,M=4/1×3+4/3×5+4/5×7+....+4/2011×2013
=2.(2/1.3+2/3.5+2/5.7+...+2/2011.2013)
=2.(1-1/3+1/3-1/5+1/5-1/7+...+1/2011-1/2013)
=2.(1-1/2013)
=2.2012/2013
=4024/2013